mesonlib: add rsplit and and maxsplit
mesonlib: add rsplit and and maxsplit

Since string has a maxsplit as well, we should implement that for
polymorphism

mesonbuild/meson,mesonbuild/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,jpakkane/meson,pexip/meson,jpakkane/meson,jpakkane/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,jpakkane/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,jpakkane/meson